In the art of weaponry, it is desired to cause a fired projectile, such as an artillery round, or other launched projectile, such as a self-propelled rocket, to explode at or near a target. The projectile is detonated by a device known as a fuze. There are three general ways in which a projected or self-propelled weapon is fuzed, viz., after penetration of the target, upon contact with the target or by fuzing at a predetermined proximity with the target. Post-penetration and contact fuzing are well established technologies which depend mostly upon mechanical sensors to determine position. Proximity fuzing is required for warheads which explode to form shaped charges such as slugs, fragments, or jets prior to contacting the target. The distance from the exploding projectile to the target to form the shaped charge is termed "standoff" and varies according to the type of weapon. Standoffs of up to 100 times the charge diameter are often needed for fragmentation delivery. Some kind of ranging device is needed on the projectile to control the proximity fuzing. Optical ranging devices carried on board projectiles are known but have features that are undesirable. For example, devices which employ separate lenses for transmiting light and for collecting light such as is found in cross beam sensor systems, are subject to errors due to triangulation effects and are inaccurate at distances greater than twenty times the lens separation distance or charge diameter. It would be desirable to provide an optical ranging device carried on board a projectile which is not subject to optical triangulation errors and can operate at greater than twenty times the charge diameter.
Pulsed laser ranging is a method for measuring distance and is based on the time required for a laser pulse to propagate to and reflect back from an object located a distance from the measuring device. It would be desirable to be able to use the principles of pulse laser ranging in a proximity fuze for a fired or self-propelled projectile.